If Busi goes, Xavi needs to experiment with Christensen or Eric as the second pivot alongside Frenkie in pre-season.
Pep uses Stones as a mobile DM in the 3-2-2-3 build-up, and he easily falls back into the CB position in defense, forming a back four with Ake at LB and Akanji at RB.
We have two problems with potential uses of Christensen/Eric in the same way. Rodri is the stationary DM, he is the Busquets, so Stones is the mobile one with a freer role. But Frenkie cannot be the stationary pivot, he needs freedom as well, so the new pivot has to be the more tactically disciplined and less adventurous one. I'm not sure whether Christensen and Eric fit that role, but they need to be tried out.
The second problem is that Balde is an aggressive wingback and would be wasted alongside the first three outfield players in the buildup. Arteta uses Gabriel-Saliba-White with Zinchenko-Partey as 3-2, Pep uses Ake-Dias-Akanji with Rodri-Stones above them. We use Christensen-Araujo-Kounde with Busi-FdJ (right now); if Busi goes and say Christensen becomes the stationary DM, we would need a new starting LCB. Maybe that's why Xavi wants Inigo as he's left-footed too.